The mitral valve in the heart of vertebrate animals is a bicuspid one-way valve situated on the left side of the heart and isolates the left atrium from the left ventricle. It comprises two leaflets of flexible collagenous material which, in normal operation, open as the left ventricle relaxes and dilates (diastole), thereby permitting oxygenated blood from the lungs to flow from the left atrium into the left ventricle. The mitral valve coapts (closes) during the contraction cycle (systole) of the left ventricle to prevent the blood from returning to the left atrium. The blood is then forced to exit the left ventricle through the aortic valve and flows to the rest of the body.
A mitral annulus, which is a fibrous ring having a malformed “D” shape supports the leaflets around their peripheries. The annulus lies in a plane generally perpendicular to the average blood flow direction through the valve. Chordae tendineae are string-like structures which extend between and link papillary muscles found on the lower portion of the interior wall of the left ventricle and the free edges of the mitral valve leaflets. These structures prevent the valve from prolapsing into the left atrium during systole.
Mitral valve regurgitation (MR) is a common heart condition caused by improper closing of the valve due to deterioration of the mitral valve and/or surrounding anatomy. MR involves the backflow of blood from the left ventricle into the left atrium during contraction of the left ventricle. As a result, the left ventricle has to pump progressively harder to circulate the blood throughout the body, thereby increasing the risk of congestive heart failure.
Currently a number of percutaneous mitral valve therapies are available to repair or replace dysfunctional mitral valves. Examples of these procedures are annuloplasty, leaflet resection, valvulotomy, valvuloplasty and leaflet plication. A common approach used to access the mitral valve for surgical procedures is through the apex of the heart via a transapical port. An incision is made in the chest wall of a patient and a catheter is advanced through the apex of the heart towards the mitral valve.
Accessing the mitral valve in this way is generally performed using radiopaque markers and fluoroscopy or other imaging systems such as intravascular sound imaging, trans-oesophageal echocardiography and angiography. Transapical access is further complicated by the presence of the sub-valvular apparatus, which includes the chordae tendineae, the papillary muscles as well as parts of the ventricular wall, which can entangle and hinder access to the mitral valve.
As it is essential to be properly positioned and orientated within the mitral valve annulus to perform surgical techniques, these techniques require specialised and expensive imaging equipment. This typically limits their application in developing and third world countries where such equipment is not readily available.
There is thus a need for cost effective and accurate methods and devices for gaining access to heart valves which do not require complex imaging techniques and equipment to perform replacement or repair surgery.